Nuclear medicine imaging is performed by injecting a radiopharmaceutical into a patient and measuring the intensity distribution of gamma radiation emitted from the patient's body. Radiopharmaceuticals are prepared by attaching a radioactive tracer to a pharmaceutical that is known to preferentially accumulate in an organ of interest. The detected radiation pattern thus provides information about the function of the organ.
A majority of current radiation detection systems utilize an “Anger”-type gamma scintillation camera for determining the radiation pattern emitted from patient's body. (The camera is named after its inventor, H. O. Anger, see, for example, “A new instrument for mapping gamma ray emitters,” Biology and Medicine Quarterly Report, U.C.R.L.-3653, 1957, which is incorporated herein by reference.) These nuclear medicine imagers use large sodium iodide scintillating crystals in conjunction with a bank of photomultipliers tubes (PMTs). A collimating aperture in front of the scintillation crystal focuses the gamma rays on the crystal, and gamma rays from a radiopharmaceutical injected into the patient produce scintillations (light flashes) in the crystal which are converted into electrical signal by the PMTs. High density shielding material, typically comprising lead, is used to cover the sides and back of the radiation detection assembly to prevent radiation from entering the detector by any path other than through the collimator. A computer locates each flash from the relative magnitudes of the PMT signals. Crystals are typically 200 to 400 square inches in area (1290 to 2580 square centimeters).
Limitations of Anger cameras are mainly caused by the conversion of scintillations into electrical signals. Sources of distortion include variation of the acceptance field-of-view angle of the PMTs with distance from the scintillation event, refraction and light guiding due to index of refraction mismatches, unavoidable dead regions between PMTs, and non-uniform spatial response of individual PMTs.
Semiconductor detector-array imagers have been proposed for solving problems with Anger cameras. For example, see U.S. Pat. Nos. 4,292,645 to Schlosser et al. and 5,132,542 to Bassalleck et al.; “Semiconductor gamma cameras in nuclear medicine,” IEEE Transactions on Nuclear Science, Vol. NS-27, No. 3, June 1980; and “Two-detector, 512-element, high purity germanium camera prototype,” IEEE Transactions on Nuclear Science, Vol. NS-25, No. 1, February 1978. All of these references are incorporated herein by reference.
Semiconductor detectors have improved camera sensitivity, particularly at 100 to 250 Kev energy levels. This improved sensitivity has led to improved energy resolution by at least factor of two over Anger cameras.
In an attempt to further improve sensitivity and accuracy, several lens constructions and materials have been proposed by Robert Smither in U.S. Pat. Nos. 5,869,841 and 5,004,319, and US Patent Application Publication 2005/0175148, all of which are incorporated herein by reference. U.S. Pat. No. 4,429,411 to Smither, which is incorporated herein by reference, describes techniques for focusing X-rays and gamma
An article entitled, “Gama WAVE: Focusing telescopes in nuclear astrophysic,” Sep. 12-15, 2005, Espace St. Jacques, Bonifacio, Corsica, which is incorporated herein by reference, provides an overview of techniques for focusing gamma rays for nuclear astrophysics telescopes.
Compton scatter cameras have been proposed to overcome some of the limitations of Anger cameras. Compton scatter cameras have been described in numerous publications, including the following, all of which are incorporated herein by reference:
Everett D B et al. in the paper entitled Gamma-radiation Imaging System Based On the Compton Effect, Proc. IEE, Vol. 124 (11), (1977), p. 995;
Cree et al. “Towards Direct Reconstruction from a Gamma Camera Based on Computer Scattering,” IEEE Transactions on Medical Imaging, Vol. 13, No. 2, June 1994, pp. 398-407; and
U.S. Pat. No. 5,175,434 to Engdahl (see the description provided with reference to FIG. 1 thereof in the Background of the Invention section).
The '434 patent describes a Compton scatter camera for nuclear medical imaging that includes an annular scattered photon detector disposed around a first scattering detector and shielded from the field of view of incident gamma photons. Scattered photons detected by the annular detector are thus scattered through angles greater than those of a conventional Compton scatter geometry.
Gamma cameras are manufactured by companies such as GE, Siemens, Hitachi, Toshiba, Philips, and Spectrum Dynamics.
All of the references (including patent references and articles) referred to herein are incorporated herein by reference.